A method and apparatus for generating microwave frequency combs based on directly modulated semiconductor lasers

Abstract

This invention discloses a method and apparatus for generating a microwave frequency comb based on a directly modulated semiconductor laser. Utilizing the direct modulation characteristics of a directly modulated semiconductor laser, an radio frequency (RF) signal is directly applied to the RF terminal of the laser. By adjusting the power of the RF signal and the bias current of the laser, the laser operates in the nonlinear region, generating optical pulses. These pulses are then processed by a photodetector to obtain the microwave frequency comb. By adjusting the frequency of the RF signal applied to the RF terminal of the directly modulated semiconductor laser, the spacing between the comb teeth is tuned. By adjusting the power of the RF signal applied to the RF terminal of the directly modulated semiconductor laser, the number and flatness of the comb teeth are optimized, ultimately resulting in a high-performance microwave frequency comb with adjustable tooth spacing and a stable spectrum.

Description

Technical Field

[0001] This invention belongs to the field of microwave photonics technology, specifically relating to a method and apparatus for generating a microwave frequency comb based on a directly modulated semiconductor laser. Background Technology

[0002] A microwave frequency comb presents itself in the form of microwave pulses in the time domain and consists of a series of discrete microwave signals with equal frequency spacing in the frequency domain. It can simultaneously provide several microwave signals of different frequencies within a certain frequency range. It not only has the characteristics of microwave signals such as light-likeness, penetrability, and non-ionization, but also has more spectral lines, a wider bandwidth, and higher spectral line spacing precision compared to single-frequency microwave signals. It has important application value in many fields such as electromagnetic compatibility testing, anti-interference testing, radar detection, satellite communication, and wireless communication, and has a very broad development prospect.

[0003] Currently, there are two main methods for generating microwave frequency combs: electrical and optical. Electrical methods primarily utilize the nonlinear effects of electrical devices or frequency synthesis techniques. Optical methods mainly involve first generating an optical frequency comb based on nonlinear effects such as four-wave mixing in optical fibers, cascaded modulators, or mode-locked lasers, and then converting this optical comb into a microwave frequency comb through photoelectric conversion.

[0004] The common problems with the above-mentioned microwave frequency comb generation schemes are that the generated microwave frequency combs have poor pitch tuning, high cost, and complex structure. Summary of the Invention

[0005] The purpose of this invention is to provide a microwave frequency comb generation method and device based on a directly modulated semiconductor laser, so as to overcome the shortcomings of traditional microwave frequency comb generation schemes, such as poor tuning and complex structure.

[0006] To achieve the above objectives, the technical solution of the present invention is: a microwave frequency comb generation method based on a directly modulated semiconductor laser, characterized in that:

[0007] The process includes the following steps: loading the radio frequency signal output from the radio frequency source onto the radio frequency terminal of the directly modulated semiconductor laser, adjusting the power of the radio frequency signal and the bias current of the directly modulated semiconductor laser, driving the directly modulated semiconductor laser to operate in the nonlinear region, generating optical pulses, and generating a microwave frequency comb by beating the pulses through a photodetector.

[0008] 2. The spacing between the teeth of the generated microwave frequency comb is equal to the frequency of the radio frequency signal applied to the radio frequency end of the directly modulated semiconductor laser, and the spacing between the teeth is flexibly adjustable; within a certain range of radio frequency signal frequency, the flatness of the generated microwave frequency comb remains stable; within a certain range of radio frequency signal power, the number of teeth and the flatness of the teeth of the generated microwave frequency comb are both adjustable.

[0009] Furthermore, the directly modulated semiconductor laser is a semiconductor laser that allows for direct modulation;

[0010] Furthermore, the radio frequency source provides a radio frequency signal of a certain frequency and a certain power, which is applied to the radio frequency terminal of the directly modulated semiconductor laser.

[0011] Furthermore, the frequency of the radio frequency signal output by the radio frequency source determines the tooth spacing of the generated microwave frequency comb.

[0012] Furthermore, the power of the radio frequency signal output by the radio frequency source directly affects the frequency range and tooth flatness of the generated microwave frequency comb.

[0013] Furthermore, the photodetector should have the characteristics of large bandwidth and low noise to ensure that the generated microwave frequency comb has a sufficiently large frequency comb range and a good signal-to-noise ratio.

[0014] A microwave frequency comb generating device based on a directly modulated semiconductor laser is characterized by comprising a directly modulated semiconductor laser, an RF source, and a photodetector; wherein the RF source is directly connected to the RF end of the directly modulated semiconductor laser to directly modulate the laser, the output port of the directly modulated semiconductor laser is connected to the input end of the photodetector, and a high-performance microwave frequency comb with configurable parameters is obtained at the output end of the photodetector by adjusting the bias current of the directly modulated semiconductor laser and the power and frequency of the RF signal provided by the RF source.

[0015] Furthermore, the directly modulated semiconductor laser allows an external radio frequency signal to directly modulate the laser.

[0016] Furthermore, the directly modulated semiconductor laser can be a distributed feedback semiconductor laser, a vertical cavity surface-emitting semiconductor laser, or a Fabry-Perot semiconductor laser, etc.

[0017] Furthermore, the radio frequency source provides a radio frequency signal of a certain frequency and a certain power, which is applied to the radio frequency terminal of the directly modulated semiconductor laser.

[0018] Furthermore, the frequency of the radio frequency signal output by the radio frequency source is equal to the tooth spacing of the generated microwave frequency comb.

[0019] Furthermore, the power of the radio frequency signal output by the radio frequency source directly affects the range of the generated microwave frequency comb and the flatness of the comb teeth.

[0020] Furthermore, the photodetector features a large bandwidth and low noise to ensure the generation of microwave frequency combs with a wide frequency range and a good signal-to-noise ratio.

[0021] Preferably, the operating temperature and bias current of the directly modulated semiconductor laser are adjusted and controlled by a temperature control module and a current control module, respectively, to ensure the stability of the laser output light wave.

[0022] Preferably, while keeping the power of the RF signal output by the RF source constant, the magnitude of the bias current of the directly modulated semiconductor laser is adjusted so that the RF signal is loaded in the nonlinear region of the directly modulated semiconductor laser. At this time, the output light is an optical pulse, which is converted into an electrical signal after photoelectric conversion. In the frequency domain, it presents a series of microwave pulses with equal spacing, thus forming a microwave frequency comb.

[0023] Compared with existing technologies, the superior effects of this invention are as follows:

[0024] One innovation of this solution is that it provides a microwave frequency comb generation method and device based on a directly modulated semiconductor laser. The microwave frequency comb is generated through current modulation technology, and the structure is simple and the operation is flexible.

[0025] One innovation of this solution is that it provides a microwave frequency comb generation method and device based on a directly modulated semiconductor laser. The method generates light pulses by applying radio frequency signals to the nonlinear region of the directly modulated semiconductor laser, and then generates a microwave frequency comb by frequency beating through a photodetector.

[0026] One innovation of this solution is that it provides a microwave frequency comb generation method and device based on a directly modulated semiconductor laser. The spacing between the comb teeth of the generated microwave frequency comb is equal to the frequency of the radio frequency signal applied to the radio frequency end of the directly modulated semiconductor laser, and the spacing between the comb teeth is flexibly adjustable.

[0027] One innovation of this solution is that the microwave frequency comb generation method and device based on a directly modulated semiconductor laser provides a stable flatness within a certain frequency range of the radio frequency signal applied to the radio frequency end of the directly modulated semiconductor laser.

[0028] One innovation of this solution is that it provides a microwave frequency comb generation method and device based on a directly modulated semiconductor laser. Within a certain range of RF signal power applied to the RF end of the directly modulated semiconductor laser, the number of comb teeth and the flatness of the generated microwave frequency comb are controllable. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of the microwave frequency comb generating device of the present invention.

[0030] Figure 2 This is a schematic diagram of a specific embodiment of the microwave frequency comb generating device of the present invention.

[0031] Figure 3 This is a schematic diagram of a microwave frequency comb with a tooth spacing of 500MHz and a bandwidth range exceeding 20GHz generated by the device described in a specific embodiment of the present invention. Detailed Implementation

[0032] The following description, in conjunction with the appendix of the present invention, Figure 1-3 The technical solutions in the embodiments of the present invention are clearly and completely described herein. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Figure 1 This invention discloses a microwave frequency comb generating device based on a directly modulated semiconductor laser, comprising a directly modulated semiconductor laser, an RF source, and a photodetector; the RF source is directly connected to the RF terminal of the directly modulated semiconductor laser to directly modulate the laser, and the output of the directly modulated semiconductor laser is connected to the input terminal of the photodetector; by adjusting the bias current of the directly modulated semiconductor laser and the power and frequency of the RF signal provided by the RF source, a high-performance microwave frequency comb is output at the output terminal of the photodetector.

[0034] Furthermore, the directly modulated semiconductor laser allows an external radio frequency signal to directly modulate the laser; the directly modulated semiconductor laser can be a distributed feedback semiconductor laser, a vertical cavity surface-emitting semiconductor laser, or a Fabry-Perot semiconductor laser, etc.

[0035] Furthermore, the photodetector must have the characteristics of large bandwidth and low noise to ensure that it generates a microwave frequency comb with a large frequency comb range and a good signal-to-noise ratio.

[0036] Furthermore, the radio frequency source provides a radio frequency signal of a certain frequency and a certain power, which is applied to the radio frequency end of the directly modulated semiconductor laser. The frequency of the applied radio frequency signal is equal to the tooth spacing of the generated microwave frequency comb. The power of the applied radio frequency signal directly affects the range and tooth flatness of the generated microwave frequency comb.

[0037] A microwave frequency comb generation method based on a directly modulated semiconductor laser, characterized in that:

[0038] The process includes the following steps: loading the radio frequency signal output from the radio frequency source onto the directly modulated semiconductor laser, adjusting the bias current of the directly modulated semiconductor laser and the voltage of the loaded radio frequency signal, driving the directly modulated semiconductor laser to operate in the nonlinear region, generating optical pulses, and generating a microwave frequency comb by beating the pulses through a photodetector.

[0039] 2. The spacing between the teeth of the generated microwave frequency comb is equal to the frequency of the applied radio frequency signal, and the spacing between the teeth is flexibly adjustable; within a certain range of the applied radio frequency signal frequency, the flatness of the generated microwave frequency comb remains stable; within a certain range of the applied radio frequency signal power, the number of teeth and the flatness of the teeth of the generated microwave frequency comb are adjustable.

[0040] Figure 2 This is a schematic diagram of a specific embodiment of a microwave frequency comb generation method and device based on a directly modulated semiconductor laser provided by the present invention. This embodiment aims to provide a microwave frequency comb generation method and device based on a directly modulated semiconductor laser. By loading a radio frequency signal into the nonlinear region of the semiconductor laser and utilizing the distortion state of the semiconductor laser during modulation, a microwave frequency comb generation method and device with simple structure, flexible adjustable comb tooth spacing, and stable spectrum is achieved. The microwave frequency comb generation device includes:

[0041] A directly modulated semiconductor laser is used as the system's light source.

[0042] The temperature control module is used to control the temperature of the directly modulated semiconductor laser, so that the temperature of the semiconductor laser remains stable during operation.

[0043] The current control module is used to apply bias current to the directly modulated semiconductor laser, perform precise current control, and drive the semiconductor laser to operate in the nonlinear region.

[0044] Radio frequency (RF) sources are used to provide RF signals with adjustable frequency and power to directly modulate directly modulated semiconductor lasers.

[0045] Optical isolators are used to ensure unidirectional optical transmission and prevent adverse effects on the light source and optical system caused by backward-transmitted light due to various reasons.

[0046] A photodetector performs photoelectric conversion on the output light of a directly modulated semiconductor laser, outputting a microwave frequency comb.

[0047] To make the technical solutions, advantages, and objectives of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0048] like Figure 2 As shown, the temperature of the directly modulated semiconductor laser is first controlled to keep it constant. Then, a bias current is applied to it using a current control module to ensure stable light output. An external radio frequency (RF) source is directly connected to the RF terminal of the directly modulated semiconductor laser, and the output RF signal directly modulates the laser. The bias current of the laser and the power of the RF signal are adjusted to load the RF signal into the nonlinear operating region of the laser. The output light then passes through a photodetector for photoelectric conversion and outputs a microwave frequency comb.

[0049] Reference Figure 2 The main device parameters were selected as follows: the operating temperature of the directly modulated semiconductor laser was stabilized at 25℃, the operating current was 22mA, and the output wavelength was 1545.264nm; the RF source was directly connected to the RF terminal of the directly modulated semiconductor laser for direct modulation, and the output signal frequency of the external RF source was set to 500MHz, and the power was set to 13dBm; the experimental results are as follows. Figure 3 As shown, the system generates a microwave frequency comb with a tooth spacing of 500MHz and a bandwidth range greater than 20GHz.

[0050] The principle of this invention is as follows: Initially, the directly modulated semiconductor laser outputs a stable light wave under the control of the temperature control module and the current control module. The radio frequency (RF) source is directly connected to the RF terminal of the directly modulated semiconductor laser through a high-speed cable. When the bias current of the directly modulated semiconductor laser is sufficiently large, an RF signal is applied to directly modulate the directly modulated semiconductor laser. The power of the RF signal and the bias current of the directly modulated semiconductor laser are adjusted so that the low level of the bias current of the directly modulated semiconductor laser plus the equivalent current of the RF signal is lower than the threshold current of the directly modulated semiconductor laser and greater than zero. At the same time, the high level of the bias current plus the equivalent current of the RF signal is greater than the threshold current of the semiconductor laser. At this time, the semiconductor laser is in a state of modulation distortion, and the output light is in the form of light pulses. The output light is then photoelectrically converted into microwave signals by a photodetector, and the frequency spectrum is in the form of a microwave frequency comb, with the comb tooth spacing equal to the frequency of the applied RF signal.

[0051] The above are preferred embodiments of the present invention. Any changes made to the technical solution of the present invention that do not exceed the scope of the technical solution of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for generating a microwave frequency comb based on a directly modulated semiconductor laser, characterized in that, The directly modulated semiconductor laser outputs a stable light wave under the control of the temperature control module and the current control module. The radio frequency (RF) source is directly connected to the RF terminal of the directly modulated semiconductor laser through a high-speed cable. When the bias current of the directly modulated semiconductor laser is sufficiently large, an RF signal is applied to directly modulate the laser. The power of the RF signal and the bias current of the directly modulated semiconductor laser are adjusted so that the low level of the bias current plus the equivalent current of the RF signal is lower than the threshold current of the directly modulated semiconductor laser but greater than zero, while the high level of the bias current plus the equivalent current of the RF signal is greater than the threshold current of the semiconductor laser. At this time, the semiconductor laser is in a state of modulation distortion, and the output light directly passes through a photodetector to generate a microwave frequency comb. The tooth spacing of the generated microwave frequency comb is equal to the frequency of the applied RF signal, and the tooth spacing is flexibly adjustable. Within a certain frequency range of the applied RF signal, the flatness of the generated microwave frequency comb remains stable. Within a certain power range of the applied RF signal, the number of teeth and the flatness of the teeth of the generated microwave frequency comb are adjustable.

2. A microwave frequency comb generating device based on a directly modulated semiconductor laser, for implementing the method of claim 1, characterized in that, It includes a directly modulated semiconductor laser, a radio frequency (RF) source, and a photodetector; wherein the RF source is connected to the RF terminal of the directly modulated semiconductor laser to directly modulate the directly modulated semiconductor laser, and the output terminal of the directly modulated semiconductor laser is connected to the input terminal of the photodetector to obtain a microwave frequency comb at the output terminal of the photodetector.

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